Question

For instance, if I have a list of words:

Words = ['A', 'list', 'of', 'words']

and want a second list to reference the lengths of those words, how could I achieve this? I’m aware that I could do something like:

Lengths = map(lambda w: len(w), Words)
[1, 4, 2, 5]

but I would have to continually call that function every time Words is altered.

Answer 1

You could use a class:

class mywords:
    def __init__(self, a):
        self.words = a
        self.length = map(lambda w: len(w), a)
    def append(self, string):
        self.words.append(string)
        self.length.append(len(string))


a = mywords(['A', 'list', 'of', 'words'])

a.append("this")
print a.words
print a.length

It’s the first time I use a class, so there might be a better way. However this seems to work well. You would need to define other methods for other operations such as insert, remove, etc.